X-ray studies of the melting and freezing phase transitions for gallium in a porous glass

We use x-ray powder diffraction to study the melting and freezing processes for gallium within a porous glass. The only modification to solid gallium was found above 20 K, in contrast with previous x-ray studies of confined gallium. The size of gallium crystallites remained nearly constant during cooling and warming, while both the melting and freezing processes were smeared. The size of confined gallium crystallites was estimated as 22 nm, which is significantly larger than the pore size. The reasons for the phase-transition broadening and hysteresis between freezing aad melting are discussed on the basis of the results obtained. [S0163-1829(98)02942-7].